Most vibration sensors of today have a flat low-frequency response curve, i.e. the frequencies below the mechanical resonance frequency of typical vibrations sensors are not damped, acoustically or any other way. For various reasons, such as for example noise or overload reasons, it is advantageous to remove, or at least damp, the low frequencies. One often used approach is to remove or damp the low frequencies electronically using an electronic filter in for example the signal processing device. However, this approach is disadvantageous in that the mechanical system of the sensor or the input stage of the signal processing device might still be overloaded by precisely the low frequency signals that the electronic filter is intended to remove. Also, electronic filters take up valuable space on the ASIC, could cause distortion of the signal and cause thermal noise which may degrade the signal-to-noise ratio. Typical prior art solutions are discussed in CN 2727712 Y and US 2011/0179876 A1.
It may be seen as an object of embodiments of the present invention to provide a vibration sensor having a predetermined low-frequency response curve.
It may be seen as a further object of embodiments of the present invention to provide an arrangement where the predetermined low-frequency response curve of the vibration sensor is not provided by electronic means.
It may be seen as an even further object of embodiments of the present invention to provide a vibration sensor having a predetermined damping of a mechanical resonance frequency.